1. Field of the Invention
The present invention is generally directed toward manufacturing methods and, more particularly, toward a method and device for reliably setting a tappet clearance.
2. Description of the Related Art
Tappet clearance is the distance between a bottom surface of an adjustment or tappet screw and an upper surface of a valve. Accurately setting the tappet clearance, which is vital to proper operation of the engine, is time-consuming and labor-intensive.
Various methods and devices for manually adjusting tappet screws are known in the art. In accordance with one conventional method, the crankshaft or cam is put in the proper angular orientation, and feeler gauges are inserted between the tappet screw and the valve stem. The tappet screw then is rotated until the screw engages the valve stem. Then a wrench is used to tighten the jam nut to hold the tappet screw in position. This manual method requires positioning the feeler gauge, adjusting the tappet screw and then tightening the nut without disturbing the position of the tappet screw. It is often difficult to accomplish all of the actions precisely and repeatably, and it is usually awkward to have all of the required tools in position simultaneously.
Further, various devices have been developed to facilitate setting tappet clearance. For example, the tool in U.S. Pat. No. 6,345,436 provides a member for rotating the screw toward or away from the valve, and means for limiting the force applied to the screw. U.S. Pat. No. 6,450,072 discloses a tool in which the tappet screw is adjusted by a hand-operated device that does not apply more than a predetermined torque limit, with a torque wrench which is used to loosen and tighten the jam nut. The proper amount of torque is achieved by the use of a clutch mechanism. This tool requires the operator to have the proper feel for the appropriate amount of torque. The operator may override the torque setting by exceeding the designated number of clicks produced by the clutch mechanism, by turning the tool too fast, or by applying excessive force to the handle. If the proper torque is not applied to the screw, the clearance will be set incorrectly. In addition, the tool requires a repetitive motion that has ergonomic deficiencies.
While these devices may operate generally satisfactorily, improvements to the process of setting tappet clearance is desired. Particularly, the known devices and methods rely upon user expertise to in order to properly set tappet clearance. As a result, the possibility of error with conventional devices is unreasonably high. Therefore, a need exists for an improved tool and method for setting tappet clearance that is less dependent on operator expertise.